Some floating vessels comprise one or more tanks for storing a liquefied hydrocarbon gas, such as LNG (Liquefied Natural Gas) or LPG (Liquefied Petroleum Gas).
WO 2010/028240 and US 2007/062430 disclose a liquid containment system for a seafaring vessel. The liquid containment system includes a tank having an at least partially non-planar upper portion. The upper portion of the tank contains a substantial portion of the liquid therein and reduces the free surface area associated with the liquid. The upper portion of the tank extends above the horizontal deck of the vessel, but still allows sufficient deck space for supporting various required equipment. In one embodiment, the liquid containment system is a membrane tank designed to receive and hold liquefied natural gas (“LNG”).
U.S. Pat. No. 4,090,460 discloses a spherical tank supporting system for low temperature liquefied gas storage tank carrying vessel. A support deck extends on a level above the bottom of a hold of a vessel carrying low temperature liquefied storage spherical tanks, from bulkheads of the hull so as to surround such spherical tanks, while a horizontal support ring projects from the outer surface of the spherical tank and is supported on the support deck through support chocks. The circular inner peripheral edge of the support deck is supported by brackets erected on the bottom plate of the hold and radially extending toward the bulkheads or by columns erected on the bottom plate of the hold. The spherical tank is of a self-supporting type (as opposed to a tank of the membrane type).
WO 2012/016295 discloses a gaseous fuel powered marine vessel. The vessel comprises at least two hulls and a portion disposed between the two hulls, a propulsion system operable using a gaseous fuel, and a storage means for containing a supply of gaseous fuel for a propulsion system, the storage means being accommodated in the portion between the two hulls. The storage means is placed in the marine vessel a significant distance aft from the bow and close to the vessel bottom.
US 2011/041753 discloses a semi-submersible offshore platform body for supporting drilling, storing, treatment or production of hydrocarbons at sea. The platform body has a cross section with a centre point in a first plane, and is defined by a side wall formed by at least one hollow side wall section. Inside the side wall section there are arranged storage tanks for storing e.g. LNG.
US 2009/293506 discloses a semi-submersible offshore structure having storage tanks for liquefied gas, which is constructed so as to improve workability in marine offloading of the liquefied gas stored in the storage tanks while reducing an influence of sloshing. The offshore structure is anchored at sea. The offshore structure includes storage tanks for storing liquefied gas, a plurality of columns partially submerged under the sea level, and an upper deck located on the plurality of columns to connect the columns to each other. The storage tanks are arranged in the columns.
Liquefied hydrocarbon gas is stored at low temperatures, e.g. LNG is handled at a temperature of −163 degrees Celsius. Thus, a tank for storing liquefied hydrocarbon gas is subjected to temperature changes as an empty tank, having the temperature of a surrounding environment, is filled with liquefied hydrocarbon gas. Due to the temperature changes a length of the tank will change, the tank contracting when filled with the cold liquefied gas.